Conventionally, in the field of printed wiring board production, semiconductor package substrate production, etc., with regard to resist materials used in etching, plating, etc., a photosensitive resin composition and a photosensitive element obtained from the photosensitive resin composition, a support, and a protective film are widely used. That is, after lamination of a photosensitive element to top of a copper substrate and pattern exposure, the cured portion is removed by a developing solution, the pattern is formed by etching (subtractive process) or plating (additive process), and the cured portion is then stripped off the substrate to give a wiring board or substrate.
Accompanying the miniaturization and increased functionality of electronic equipment in recent years, there has been a demand for an increase in the wiring line/space (L/S) density. There is also a desire, from the viewpoint of improving the workability, for a photosensitive resin composition that has high sensitivity and low plating bath contamination.
High sensitivity photopolymerization initiators are disclosed in German Patent No. 2,027,467, EP-A-11,786, EP-A-220, EP-A-589, JP-A-6-69631, etc. Furthermore, U.S. Pat. No. 3,479,185 discloses a photosensitive resin composition in which high sensitivity is achieved by a combination of a hydrogen-donating compound and a 2,4,5-triarylimidazole dimer, which is a photopolymerization initiator that gives little plating bath contamination.
However, the high sensitivity photopolymerization initiators disclosed in the above-mentioned specifications have the problem of plating bath contamination, and the case in which the 2,4,5-triarylimidazole dimer is used has the problem that if the amount thereof used is increased in order to adjust to a required sensitivity, then the resist line width increases, and if the amount of hydrogen-donating compound is increased, then the adhesion to copper and the storage stability deteriorate.